Hydrophobic interaction of V12 bowl-type dodecavanadates with alkyl ammonium cations

Abstract

The V12 dodecavanadate, [V12O32]4−, that is one of a dominant polyoxovanadate species in non-aqueous media, was investigated focusing on the interaction of alkyl chains on its counter cations. Although the presence of such a species is not reported in any biological system, the unique V12 bowl anions have exhibited a host-guest property to accommodate a biologically active anion such as a halide, a cyanide or an azide for its delivery to the system. The nonpolar interactions between alkyl chains and the surface oxygen atoms on the V12 is of significance in the host-guest property and the reactivity of the V12. In the solid state, a tetraethyl ammonium (TEA) cation approached 3 Å above the cavity of the V12 via non-covalent interaction showing the lid effect. This interaction induces a distortion of its flexible framework even in a solution state. From the solution state 51V NMR and IR spectra, the orientation of an azide in the cavity was altered between TEA and tetra-n-butyl ammonium (TBA) salts. The modification of the non-covalent interaction also affected an oxidative catalytic performance with H2O2. The rate of the formation of active species of a TEA salt of [V12O32(Br)]5− was shorter than that of a TBA salt.